In general medicine and its specialties it is logical that the rare cases are extraordinary, singular or unusual. But in our specialty in particular, we have to differentiate between the infrequent and the rare cases.

It is not frequent for psychiatrists to see in the daily basis pathologies associated with organic, metabolic or infectious diseases (depression associated with psoriasis, delusional parasitic disease, and psychosis after cerebrovascular accidents, etc.) but if detected we do not consider them to be rare [1].

But, on the other hand, we do have the rare manifestations in psychiatry. That we barely detect them must be relate with three factors mainly:

1. With the criteria for psychiatric illness that relate: a) Symptoms, b) Evolution in the time of disease (pathocronia), and c) The pathoplasty (form of modelling or presentation of diseases).

2. With the emergence of psychiatric medications.

3. With the globalization of the DSM diagnostic criteria (APA criteria) and ICD (WHO criteria).

Then let's look at these three points.

With the Criteria for Psychiatric Illness Relating: a) Symptoms, b) Evolution in the Time of Disease (Patocronia), and c) Pathoplasty

Emil Kraepelin (1856-1926) had the innovative idea of creating a psychiatric taxonomy (classification of the disorders) taking into account the symptoms of the disease and at the same times its evolution (pathocronia). This is the basis of our current classifications. A patient who suffers depressive symptoms after the death of a family member can be mourning, but if the symptomatology became long and/or severe we´ll diagnose a depressive disease. If once cured, it suffers from repeated depressions in successive years we will conclude in a diagnosis of recurrent depression. Also in a patient who suffers delusional symptoms for 10 days, we can´t know if it is an acute delusional disorder or if over time it will become a chronic delirium or schizophrenia. The evolution over time of the disease is crucial to consolidate our diagnosis (pathocronia). But it is fundamentally due to the pathoplasty the fact that we find few rare diseases. Many psychiatric illnesses are adapted in its manifestations to the existing socio-cultural background. For instance, nowadays it will be rare if we saw a case of Lycanthropic delusion (experience of transforming into a Wolf) which was much more frequent for 150 years. But back then no patient did not feel extra-terrestrial powers nor that were they being controlled by chips or microphones (since these devices did not exist). What current psychiatrist has seen any patient who believes to be Napoleon? It is rare these days. But now, some patients experience the television relating to them, which did not happen before.

Therefore the rarity of some of our current psychiatric manifestations appears when ancient characteristics are manifested in their pathoplasty.

With the Emergence of Psychiatric Medications

From the emergence of psychotropic drugs, mainly since half of 20th century, many of the clinical manifestations that were frequent until then disappeared. These are the cases of Prosectic (Proskinetic) catatonia, the schizophasia, some severe depressions as Cotard syndrome, or the Stauder’s "Mortal Catatonic" Syndrome. A maniac-stupor condition is very rare to see nowadays. That typical film image of the mentally ill wandering in the psychiatry room with stereotypies or Echo phenomenon (echolalia, echopraxia-echokinesis, echomimia, etc.) is more of an old clinic that one of today.

With the Globalization of the DSM Diagnostic Criteria (APA: American Psychiatry Association) and ICD (WHO)

The DSM and ICD international classification systems have eliminated the concept of disease and widespread of "disorder".

The reality is that these systems sought to be very operating but nothing personified in relation to the patient. For them there are more diseases than patients. Since they look for certain 'objectivity' and to group together the same type of patients worldwide with the same criteria, they have been generalizing our diseases. One major depressive disorder or a generalized anxiety indicates that the diagnostic criteria are met but says nothing of the patient.

In this sense, Traver pointed out how arbitrary multiplication of the DSM criteria does not, but swells, the list of diseases that can be diagnosed and treated, and worse: No criteria between these shifting sands that separate normal and adaptive to the pathological.

We have raised the problem of rare diseases in Psychiatry but, with Gustavo Tolchinsky, we can paraphrase to Huxley and conclude saying that the problem is not the rare diseases in Psychiatry but that "medical science has advanced so much that almost there is nobody completely healthy" [2].